Nagy & Cone (Vision Research, 1996) report the asymmetry that search for a more saturated target among less saturated distractors is easier than search for a less saturated target among more saturated distractors. The Saliency Model (Rosenholtz, Perception & Psychophysics, 2001) predicts that this asymmetry is due to the background color of the display relative to the target-distractor colors, and that appropriately changing the background color should reverse the color search asymmetry.

Observers searched for a known target among homogeneous distractors. The stimuli consisted of 0.14 deg. diameter disks at random locations within a 4.25 deg. diameter area. We measured the time for an observer to depress a response button indicating that they had determined whether a target was present. Seven equiluminant target-distractor pairs were used, ranging from unsaturated white to saturated red, with each member of a pair serving as target and distractor in different blocks of trials. Each pair was presentedon both achromatic and red backgrounds of a lower luminance.

With an achromatic background, reaction times were shorter when the target was more saturated than the distractors. When the same stimuli appeared on a red background, the asymmetry reversed. On both

Both the direction and magnitude of a color search asymmetry depend upon the background color. Several models qualitatively predicts these results, including both the Saliency Model and a signal detection theory model in which the viewer observes the color difference between each element and the background, with noise proportional to the magnitude of the difference.